Summary:MgGd0.1Fe1.9 O4 ferrite with improved electrical and dielectricproperties has been synthesized by conventional ceramic technique. X-rayanalysis explains the single-phase inverse spinel structure of the ferrite. Thedc resistivity is increased by arrangement of magnitude as compared toMagnesium ferrite. The dielectric loss of the model explained that at roomtemperature is only 3 × 10?3 at 3 MHz. If th resistance is high andlow dielectric loss that can be complementary to better constitutionalStoichiometry, size and character of the additives.
The variation of dielectricproperties of the model as a purpose of frequency in the class 0.1–20 MHz hasbeen deliberate at different temperatures. The electric and dielectric propertyhas been studied as a purpose of temperature. Possible methods participating tothe results have been explained slightly in the paper.1. Introduction: Spinel ferrites have been studiedextensively because they play a vital role in the technological applications.Gd–Mg ferrites have emerged as one of the most important material due to itshigh dc resistivity and low dielectric losses. It is very important in manyapplications to control the dc resistivity of the spinel ferrites.
For thispurpose two major possibilities are available, controlling the sinteringtemperature and substitution. The dc resistivity of MgGd0.1Fe1.
9O4ferrite is increased by one order of magnitude as compared to Mg ferrite. Theseuseful properties of the spinel ferrites depend upon the choice of the cationalong with Fe2+, Fe3+ ions and their distribution betweentetrahedral (A) and octahedral(B) sites of the spinellattice, preparation methods, chemical com-position, sintering temperature,rate of sintering and nature of the additives. All the ferrites have high dcresistance. It is used in the formation of the transformers central parts andchokes. All the ferrites having extremely low dielectric loss are very helpfulfor microwave statement. In the paper ,the difference of electric anddielectric properties of the model as a purpose of frequency at variedtemperatures. In addition to this, the effects of temperature on the electricand dielectric properties were investigated and reported in the present work.
2. Experimental details: Mg–Gd ferrite ofcomposition MgGd0.1 Fe1.9 O4 was prepared byusing the standard ceramic technique. Analytical grade reagents MgO, Gd2O3 and Fe2 O3 were weighted in appropriateproportions and mixed thoroughly by wet blending with de-ionized water in anagate mortar and pestle. The mixed powders were dried and calcinated at 800 ?C for 3 h to improve the homogeneity of the constituents. After cooling to roomtemperature the samples were mixed with a small quantity of polyvinyl alcoholas a binder and milled.
The powders were compressed into pellets uniaxiallyunder a pressure of 3–8 ton/in.2 in a stainless steel die. Thepellets were finally sintered at 1000 ? C for 3 h and were cool downto room temperature. The single-phase nature of the prepared samples was checkedby X-ray diffraction studies, which were made by Cu-K radiation of wavelength1.54 Å using Riga Ku-Denki X-ray diffraction meter. The surfaces of the pelletwere polished and coated with silver paste; they acted as good contacts andelectrodes for measuring the electric and dielectric properties. The dielectricconstant and dielectric loss were determined by Agilent Technologies 4285A PrecisionLCR meter at room temperature in the frequency range from 0.075 to 20 MHz.
Thedc resistivity of the samples at different temperatures was measured by using aKeithley Model 2611 in the temperature range 293–473 K.3. Results and discussion: The X-ray diffractionpatterns for the ferrite powder obtained on calcination at 1000 ? Ccorresponded to that of the single-phase inverse spinel structure for thecompositions MgGdx Fe2?x O4 (x= 0.00 and 0.1). The diffraction peaks are quite sharp because of themicrometer size of the crystallite. The particle size of the sample has beenestimated from the broadening of XRD peaks using the Scherrer equation.
Theaverage particle size is about 0.1–1 m at 1000 ? C. The variation ofdc resistivity with temperature. High dc resistivity of ?7× 108_cm is obtained at room temperature, and decreases with increase in temperature.
The higher value of dc resistivity is due to Gd3+ content in Mgferrite. Gd3+ content doping reduces the iron ion concentration from2 to 1.9 thereby reduces the number of Fe3+ ions on theoctahedralsites which play a dominant role in the mechanism of conduction. The insetshows the variation of dc resistivity of MgFe2O4 (Pure Mgferrite) with temperature. The resistivity of the sample decreases withincrease in temperature according to Arrhenious equation .
Increasingtemperature leads to decrease in resistivity, which is the normal behavior ofsemiconducting materials. Increase in temperature of the sample will help thetrapped charges to be liberated and participate in the conduction process, withthe result of decreasing the resistivity. This decrease in resistivity could berelated to the increase in the drift mobility of the thermally activatedelectrons according to the hopping conduction mechanism and not to thermallycreation of the charge carriers. The hopping conduction mechanism between Fe2+? Fe3++e?1 is the main source of electron hoppingin the process. Activation energy, E was calculated from the slope ofthe graph. The value of activation energy for the sample is 0.
4497 eV. Inferrite samples, the activation energy is often associated with the variationof mobility of charge carriers rather than with their concentration. The chargecarriers are considered as localized at the ions or vacant sites and conductionoccurs via a hopping process. The hopping depends upon the activation energy,which is associated with the electrical energy barrier experienced by theelectrons during hop-ping.
The variation of dielectric constant as purpose offrequency in the range 0.1_20 MHz at various temperatures. Initially dielectricconstant decreases slowly with frequency up to 1 MHz and becomes almostconstant up to 6 MHz. The increase in dielectric constant above 6 MHz mayindicate the beginning of a possible presence of resonance with peaks occurringat higher frequencies. The initial decrease in dielectric constant withfrequency up to (1 MHz) can be explained by the phenomenon of dipolerelaxation. The resonance may arise due to the matching of the frequency ofcharge transfer between Fe2+ ? Fe3+ ions, and that of theapplied electric field. These changes can also be elaborated on the basis ofspace charge polarization model of Wagner and Maxwell .
The variation ofdielectric constant with temperature at different frequencies. The dielectricconstant increases with temperature at all frequencies. The hopping of thecharge carriers is thermally activated with t he rise in temperature; hence,the dielectric polarization increases, causing an increase in dielectricconstant. At lower frequencies (100 kHz), the increase in dielectric constantis very large with an increase in temperature, while at higher frequency range(1–12 MHz), the increase in dielec-tric constant is small.
The dielectricconstant of any materials, in general, is directly related to dielectricpolarization. The higher the polarization, the higher the dielectric constantof the mate-rial. There are four primary mechanisms causing polarizations:electronic polarization, ionic polarization, dipolar polarization and spacecharges polarization. Their occurrence depends upon the electric frequency ofthe applied field. At low frequencies, space charges polarization and dipolarpolarization are known to play the vital role 19and both these polarizations are temperature dependent. At high frequencies,ionic polarizations are main contributors, and their temperature dependence isinsignificant.
The change of dielectric loss with frequency at differenttemperatures. The dielectric loss factor decreases initially with increasingfrequency followed by the appearance of a resonance with peaks occurring athigher frequencies. The initial decrease in dielectric loss (tan ?) with anincrease in frequency is in accordance with the Koops phenomenological model. Theresonance may arise due to the matching of hopping frequency with the frequencyof the external electric field. Hudson has shown that, the dielectric losses inferrites are reflected in the conductivity measurements where the materials ofhigh conductivity exhibiting higher losses and vice-versa.
The change ofdielectric loss as a function of temperature at different frequencies. Thedielectric loss also shows the same trend as the dielectric constant curves,and can be explained online similar to those advanced for explaining dielectricconstant. The low values of dielectric constant, dielectric loss and high valueof dc resistivity are due to the Gd3+ ion content in Mg ferrite.This result is explained in view of the hopping conduction mechanism between Fe2+? Fe3+ + e?1, Gd3+ ions do notparticipate in conduction and polarization process but limit the degree ofhop-ping by blocking up Fe2+ ? Fe3+ + e?1pattern on the octahedral sites. This is due to the reduction in theconcentration of Fe ions inthe system due to the doping of Gd3+ ionsin Mg ferrite.4. ConclusionsSingle-phase MgGd0.
1Fe1.904ferrite has been synthesized by conventional ceramic method. The particle sizewas calculated from the most intense peak (3 1 1) using the Scherrer equation.The dc resistivity studied shown that ferrite is increased by one order ofmagnitude as compared to undoped Magnesium ferrite.
High value of dcresistivity makes this ferrite suitable for the highfrequency applicationswhere vortex current losses become appreciable. Gd–Mg ferrites may be used intelevision yokes and fly back transformers because of their higher resistivitywhich eliminates the need for taped insulation between yoke and winding.Temperature dependent dc resistivity decreases with an increase in temperatureensuring the normal behavior of semiconducting materials.
The value of dielectricloss in the presently studied ferrite at room temperature is only 0.003 at 3MHz. Low values of dielectric constant and dielectric losses exhibited by thisferrite suggest its utility in microwave communications.